This invention relates to an electric discharge machine using a wire electrode.
A conventional electric discharge machine of this type is as shown in FIG. 5. In FIG. 5, reference numeral 12 designates a workpiece to be machined; 10, a movable table on which a workpiece is placed; 16 and 20, sliding members; 14 and 18, driving means for moving the sliding members 16 and 20, namely, servo motors; 22, a numerical control device for applying signals to the servo motors 14 and 18; 24, a machining wire electrode; 30 and 32, wire guides for supporting the machining wire electrode 24; 26, a wire bobbin on which the wire electrode 24 has been wound; 36, tension rollers for winding the wire electrode 24; 38, a wire take-up roller on which the wire electrode used is wound; 28 and 34, voltage applying elements for applying voltage across the wire electrode 24 and the workpiece 12; 40, an electric power supply unit for supplying the voltage; 42, a DC source; 44, a switching transistor for switching on and off the DC source 42 to provide a pulse voltage; 50, a control unit for controlling the operation of the switching transistor 44; 48, a limit resistor; 46, a charging capacitor; 52, a machining solution device; 56, a machining solution tank in which a machining solution is stored; 58, a filter for the machining solution; 60, a pump for pumping out the machining solution; 62, a nozzle for supplying the machining solution to the workpiece; 54, the machining solution serving as a discharge medium between the workpiece 12 and the wire electrode 24; and 70, an automatic wire electrode feeding device capable for cutting and connecting the wire electrode 24.
The operation of the electric discharge machine thus organized will be described with reference to FIG. 5.
The workpiece 12 is fixedly set on the movable table 10. The movable table 10 is moved in the X-axis direction by the servo motor 14 and in the Y-axis direction by the servo motor 18 under the control of the numerical control device 22; that is, the movable table 10 is positioned by the servo motors 14 and 18. The pulse voltage V which is converted from the output voltage of the DC source 42 with the aid of the switching transistor 44 and the charging capacitor 46 in the power supply unit 40, is applied through the feeders 28 and 34 to the wire electrode 24. On the other hand, the machining solution 54 passing through the filter 58 in the machining solution supplying device is pumped out of the machining solution tank 56 and applied, as a discharge medium, between the workpiece 12 and the wire electrode 24.
As a result, electric discharge occurs between the wire electrode 24 and the workpiece 12, thus producing heat in the latter. Therefore, as the wire electrode 24 and the workpiece 12 are moved relative to each other by means of the numerical control device 22, the workpiece 12 is machined as required.
A plurality of parts (configurations) may be formed by machining one workpiece 12 with the automatic wire electrode supplying device 70 as follows: As shown in FIG. 6, at each of initial holes 1 through 8, the automatic wire electrode supplying device 70 is operated to automatically connect the wire electrode 24, and a workpiece cutting operation is started. In this case, an NC program is executed as shown in the part (a) of FIG. 7. That is, slightly before the part is completely cut out of the workpiece; i.e., when the cutting of the workpiece has been not yet completed so that the part may not be dropped from the workpiece, the automatic wire electrode supplying device 70 is operated to cut the wire electrode 24 with a cut-left portion, and the same cutting operation is then carried out from the following initial hole. Thus, the unmanned cutting operation can be continuously carried out.
Upon completion of the series of cutting operations, an NC program as shown in the part (b) of FIG. 7 is executed to machine the remaining parts of the cutting loci.
In the part (a) of FIG. 7, reference character M21 designates a wire electrode cutting instruction. In response to the instruction M21, the discharge machining operation is suspended. In the part (b) of FIG. 7, reference character M0 designate a program stop instruction. In response to the instruction M0, the machining of the remaining part of the cutting locus which the cut-leaving NC program has left so as to be machined later (hereinafter referred to as "a cut-left", when applicable) is suspended. In the parts (a) and (b) of FIG. 7, the solid lines indicate what are cut by electrodischarge machining.
The conventional wire cut discharge machine is constituted as described above. Therefore, in the case where a plurality of parts are successively cut out of a workpiece as shown in FIG. 6, it is necessary to use two NC programs such as a cut leaving NC program as shown in the part (a) of FIG. 7 and a cut completing NC program as shown in the part (b) of FIG. 7. It takes time to form the two NC programs, and it is necessary to store the NC programs in the numerical control device. That is, the conventional discharge machine is low in work efficiency. In addition, it may suffer from a difficulty that the memory is not effectively utilized.